214 MR. R. OWEN ON THE STRUCTURE OF THE HEART 
observes with respect to its external form, that in Salamandra, Triton, Siren pisci- 
formis, and Sir. lacertina ‘‘the auricle is divided by a strong contraction into an anterior 
larger, and a posterior lesser moiety ;”' and then proceeds to state that in the genus 
Pipa he finds ‘a very interesting transition-structure in a membranous velum, which 
extends from the floor of the ventricle to the upper and posterior wall of the auricle, 
where a manifest opening is left.’’? 
My own dissections have, however, satisfied me of the correctness of Dr. Davy’s 
ascription of a distinct auricle for the pulmonic blood to the common Frog and Toad?; 
and the more recent researches of Dr. Martin St. Ange* have shown, that not only do 
the Anourous Caducibranchiata recede from the character assigned by Cuvier to the 
Batrachian order, but that in the Salamanders also there exists a small but distinct 
pulmonic auricle. 
In justice to Mr. Hunter it must be observed that he had accurately ascertained the 
true structure of the heart of the higher Batrachia, and included the Frogs, Toads, and 
Salamanders, with Serpents and the higher Reptiles, in the class which he denominates 
Tricoilia®, from the heart being composed of three cavities. The Siren, the Amphiuma, 
the Kattewagoe or Menopoma of Harlan, in short, all the Reptiles douteux of Cuvier that 
Mr. Hunter was acquainted with, he considered as a distinct class, which he denomi- 
nates Pneumobranchia in the manuscript which is quoted by Rusconi in the work entitled 
‘Amours des Salamandres Aquatiques’®, and which is now published in the ‘ Physio- 
logical Catalogue of the Hunterian Collection’’. Neither Rusconi, Cuvier, Meckel, nor 
Hunter, who have severally made one or more of the doubtful Reptiles the subjects of 
particular investigation, has suspected that these remarkable animals resemble the 
higher Reptiles in the number of cavities of which the heart is composed; but they 
appear to have been uniformly regarded as approximating Fishes, as well in the sim- 
plicity of the circulating organ as in the permanence of a greater or less proportion of 
the branchial apparatus. 
In the progress of the arrangement and description of the preparations of the circu- 
lating organs which are preserved in the Gallery of the Museum of the Royal College 
of Surgeons, I have had occasion to dissect an Amphiuma means, a Proteus anguinus, and 
a Siren lacertina, in order to reconcile the appearances presented by the Hunterian pre- 
parations with published descriptions, and more especially with that of the Siren lacer- 
tina, given by Mr. Hunter himself in the 56th volume of the ‘ Philosophical Transac- 
tions’*. In all these animals I find the pulmonary veins terminating in a small but 
' «Der Vorhof—durch eine starke einschniirung in eine vordere, grossere und eine hintere, Kleinere Hilfte 
getheilt ist.”—Loc. cit., p. 216. 
2 «So eben finde ich indessen bei einem frischern Exemplar eine interessante Uebergangsbildung in einem 
hautigen, senkrechten Segel, das sich von der Grundfliche der Herzkammern bis zum obern und hintern Rande 
der Vorhéfe erstreckt, hier aber eine deutliche Liicke liisst.”—Loc. cit., p. 217. 
* See the Zool. Journal, vol. ii. p. 586. * Table of the Circulating System. 
5 On the Blood, p. 135. i IP 7 yol. ii. p. 145. 8 1766. p. 308. 
